FWIW--the manual for the Blue Sky 2000 has a good
explanation of when MPPT helps the most.  It is
on page 5 of this manual:
http://www.blueskyenergyinc.com/uploads/pdf/Manual_BSE_SB2000.pdf

Briefly, the colder the panel and the lower the battery
voltage, the more MPPT helps.  For hot temps and batteries
that are not deeply discharged, MPPT might not be worth
the extra price over simple PWM.

Of course, you can buy a 12V 10 A MPPT controller on ebay
for $12.57!

Richard